Pitch treatment means

ABSTRACT

A spinnable pitch, useful in the manufacture of carbon filaments of continuous lengths, is prepared by the multiple solvent extraction of pitch, first by trituration of pitch particles with a low-boiling, aromatic solvent in which the bulk of pitch particles is essentially insoluble - then by dissolution of the pitch in a solubilizing solvent, filtration, and evaporation of the solvent.

United States Patent Shea et a1.

[ 1 June 6, 1972 [54] PITCH TREATMENT MEANS [72] Inventors: Frederick L.Shea, 806 Wedgewood Rd; Louis A. 100, 208 Chicksaw Dr., bah of JohnsonCity, Tenn. 37601; Thomas W. Martin, P.O. Route 6, Elizabethton, Tenn.37643 [22] Filed: Oct. 28, 1970 [21] Appl.No.: 84,883

2,871,181 l/l959 Kulik ..208/45 2,953,501 9/1960 Mipone ..208/453,079,326 2/1963 Neuworth ..208/45 3,200,062 8/1965 Britton 208/453,278,415 10/1966 Doberenz et a1 ..208/45 3,373,101 3/1968 Folkins eta1. ..208/45 Primary Examiner-Delbert E. Gantz AssistantExaminer-Veronica OKeefe Att0rneyDona1d R. Cassady [57] ABSTRACT Aspinnable pitch, useful in the manufacture of carbon filaments ofcontinuous lengths, is prepared by the multiple solvent extraction ofpitch, first by trituration of pitch particles with a low-boiling,aromatic solvent in which the bulk of pitch particles is essentiallyinsoluble then by dissolution of the pitch in a solubilizing solvent,filtration, and evaporation of the solvent.

6 Claims, No Drawings BACKGROUND OF THE INVENTION Carbon fibers havebeen produced from organic polymer fibers such as rayon orpolyacrylonitrile by oxidation and carbonization of the fibers. The sameprocess has been found to be applicable to manufacture carbon fibersfrom filaments of polyvinyl chloride, polyvinyl acetate, blown asphalt,and petroleum pitch.

Otani, U.S. Pat. No. 3,392,216, July 9, I968, discloses and claims amethod for the heat treatment of several of these pitch-like materials,particularly polyvinyl chloride. The Otani method involves heating thestarting material to 300-400 C. in an inert atmosphere to raise thesoftening point and improve the molecular weight range of the pitch-likematerial.

Coal tar pitch is particularly difiicult to use because of the presenceof an insoluble second-phase material which must be removed prior tospinning. If allowed to remain when the fiber is drawn from thespinnerette, the particles of second-phase material will form stresspoints in the filament which tend to lower the strength of the filament.Nodules on the surface of the filament will render the filamentunacceptable for use in certain applications.

More recently a method has been devised for treating a coal tar pitch toenable the pitch to be spun into continuous lengths capable of beingoxidized and carbonized into commercially acceptable carbon fibers. Suchtreatment includes l dilution of the pitch with quinoline or lightcreosote oil, (2) filtration, (3) evaporation of the diluent, and (4)heat treatment of the pitch within the range of about 280-305 C. until asoftening point of 230260 C. has been attained, usually from 40 to 140hours. The pitch can then be spun, oxidized, and carbonized as in theprior art. This method leads to a relatively clean pitch of about 80percent carbon yield after appropriate processing of the spun filamentwhich will form 0.5 l mil continuous filament.

These carbonized filaments have a tensile strength of 80,000 to 130,000psi, a volume resistivity of l,280l ,600 micro-ohm inches, and anapparent density of about 1.65 g./cc. They are useful as substrates forboron deposition, and as fillers for carbon-carbon, carbon-resin,carbon-metal composites and other similarapplications where filamentarycarbon is conven-tionally and advantageously employed.

This invention relates to an improved method of preparing a spinnablepitch-like material from pitches of petroleum, coal tar, and thepyrolysis of organic polymers origin.

More particularly this invention relates to a method of preparing suchpitch-like material without subjecting the pitch precursor to heattreatment to raise the softening point, thus avoiding the potential forsecond phase carbon formations.

Fibers prepared from the pitch and oxidized and carbonized in the usualmanner have improved characteristics.

SUMMARY OF THE INVENTION By the process of this invention, a pitch fromcoal tar or petroleum, petrochemicals and the pyrolysis or organicpolymers is l fabricated into small particles capable of being actedupon by an appropriate solvent to remove therefrom low boiling, lowmolecular weight material; 2) the resulting particles are contacted withsuch an essentially aromatic or equivalent solvent to remove such lowboiling, low molecular weight materials at a temperature from aboutambient room temperature to about the softening point of the pitch incontact with the solvent; (3) the particles are separated from thesolvent; 4) the particles are then extracted with a solubilizingsolvent; (5) the resulting suspension is filtered to remove theinsoluble solid materials therefrom, and (6) the solvent of the secondextraction is evaporated from the resulting filtrate to yield aspinnable pitch. In an obvious alternative, steps 1, 2, and 3 areremoved until after the performance of step 6. That is, (l) the rawpitch is extracted in a solubilizing solvent; (2) filtered to remove thesolid materials therefrom; (3) the sol vent is removed by evaporation;(4) the resulting solid or liquid filtered pitch is ground if necessary;(5) extracted by an appropriate solvent to remove the low-molecularweight components; and (6) separated from the extract. The pitch, whenprepared by either of the above methods, need not be subjected toheating over long periods of time and is of a physically more uniformnature with respect to softening point and homogeneity than is a heattreated pitch. The filaments manufactured therefrom when carbonized to1,200 C. or above are stronger than those prepared from heat treatedpitches.

DETAILED DESCRIPTION OF THE INVENTION Otani, in Japanese patentspecification No. 2511/69, discloses a method for the preparation of aspinnable pitch from coal tar. By the method of the patent, coal tarpitch is either melted or solubilized in chloroform and filtered toremove the second-phase material. It is then destructively distilled ata temperature not exceeding 250 C. for several hours and then vacuumdistilled at about 300 C. Otani states that the distillation stepaccomplishes the removal of low molecular weight components.

By the herein-described method, only selected low molecular weightcomponents, only those soluble in benzene or equivalent solvents areremoved. Additionally, there is no thermal rearrangement,polymerization, or aromatization of the coal tar pitch generally foundas a result of any heat treatment process. This method affords a productparticularly suitable for spinning, oxidizing, and carbonizing to yielda superior filamentous product.

The first step of the herein-described method is to mechanically orotherwise form the pitch into small particles, of the order of -l00mesh. This can be done most conveniently by grinding or milling solidpitch or by nebulizing or atomizing a molten pitch and rapidly coolingthe droplets to below their softening point so as to preventcoalescence. This nebulization can be accomplished in the presence ofthe aromatic or equivalent solvent useful for the subsequent process ofthis invention.

The above-formed pitch particles are then extracted by a selectedsolvent in such a quantity that from about 10 to about 30 percent of thepitch is extracted into the solvent, the soluble portion of the pitchbeing the low molecular weight components thereof. The choice of solventand solvent volume is determined by the desired softening point range ofthe final pitch product. As for example, a pitch solubilizing solvent,quinoline, used in a solvent to pitch ratio of 1:l (V/V) is adequate anda non-solubilizing solvent, benzene, in a 1:l (V/V) ratio issatisfactory to the practice of this invention. It is preferred to use asolid to solvent ratio of about 1:5 (V/V) when benzene is used as asolvent. The extraction can be carried out at from about the freezingpoint of the solvent to about the softening point of the pitch. Ideally,since the solvent can be recovered and reused, safety and economicsdictate the use of a relatively large volume of solvent at or about roomtemperature. We have found that about l-lO volumes of benzene per volumeof pitch is capable of performing the extraction depending upon thetemperature at which the extraction is carried out.

The solvent and solid pitch are then separated by filtration,centrifugation or the like separative means. Preferably, any residualsolvent contained in the pitch is removed therefrom prior to furthertreatment of the pitch such as dissolution of the pitch in the secondsolvent by the method of this invention. This solvent removal can beeffected by the usual vacuum stripping or evaporative techniques carriedout at or below atmospheric pressure. It is advantageous to use vacuumremoval of the solvent in order to raise the relative vapor pressurethereof.

The resulting solid pitch particles are then dissolved in a sufficientquantity of a pitch solubilizing solvent to dissolve at least 45 percentof the pitch based upon the total quantity of starting pitch. Thisdissolution can be accomplished at from the freezing point to the refluxtemperature of the solvent.

The solvent useful for this dissolution can be the same or a differentsolvent from that used in the first extractive step. If the solvent isthe same, it is obvious that a greater quantity of solvent will benecessary and/or a higher temperature will be required to carry out thedissolution at this point. If the solvents are different, the volume andtemperature of dissolution are so chosen to provide a pitch of theproper softening range and physical characteristics. For example, ifbenzene is used as a solvent, a solvent-pitch ratio of 4:1 (V/W) isappropriate for the first extraction at room temperature, and asolventpitch ratio of 50:1 (V/W) at reflux temperature is useful for thesecond extraction to provide a final product having a softening range of240-260 C. from a 150 C. softening point starting pitch. The same effectcan be accomplished by using a benzene solvent in 5:1 solvent-pitchratio and a quinoline solvent in :1 solvent pitch ratio for the twoextractive steps.

The next step in the purification process is the separation of thesecond-phase insoluble material, commonly called quinoline insolubles,from the pitch-solvent mixture. This separation is carried out byfiltration, centrifugation, or similar separation technique.

The filtrate is then stripped of the solvent. The stripping operation ispreferably carried out at less than atmospheric pressure in order toavoid heating the pitch to a temperature at which rearrangement andcracking can occur. Thus, for example a quinoline-pitch (10:1) mixtureis heated for about 8.5 hours, ultimately attaining a temperature of 235C. at 0.15 mm. (in.) in order to completely remove the quinolinetherefrom.

Solvents useful for the dissolution steps of this invention includeacetone, benzene, toluene, o, m, p-xylene, Tetralin, methyl ethylketone, quinoline, isoquinoline, indole, pyridine, quinoxaline,pyridine, pyrimidine, pyrazine, 01-, and ,B-methylnaphthylene, dimethylformamide, dimethyl acetamide, dimethylsulfoxide, dimethylsulfone, andthe like, and mixtures thereof in appropriate concentrations to carryout the manipulative steps as required by this invention.

A more complete understanding of the process of this invention can beobtained by reference to the following examples which are illustrativeonly and not meant to limit the scope thereof which is fully expressedin the hereinafter appended claims.

' EXAMPLE 1 v A coal tar pitch with a softening point of about 187 C.(ring and ball A.S.T.M. D-36) is ground to -100 mesh size. Four hundredgrams of this pitch is triturated with 2 liters of benzene at roomtemperature for 10 minutes.

The suspension is filtered, and the filter cake washed with 300 ml. ofhexane and dried in vacuo for 4 hours. A residue of 294 g. is obtainedwhich is mixed with 2,940 g. of quinoline for 10 minutes at 60-70C. Thesuspension is filtered using 25 g. of diatomaceous earth as a filteraid.

. The filter cake is washed with 400 ml. of quinoline and the quinolineis added to the previous filtrate. The combined filtrates are evaporatedin vacuo to yield 195 g. of a pitch suitable for melt spinning.Softening point: 270280C.

EXAMPLE 2 A coal tar pitch of similar origin to that of Example 1 10 g.)is extracted by stirring with 100 ml. of quinoline at about roomtemperature for one hour. The mixture is filtered and the residue washedwell with 10 ml. of quinoline. The filtrates are combined and thesolvent removed therefrom by evaporation in vacuum.

The resulting residue is ground to 100 mesh and extracted by stirringinto 4 volumes (W/V) of a mixture of benzenehexane (3:1).

The solvent is removed and the residue dried in a vacuum oven for fourhours to yield a spinnable pitch. Softening point: 2l0-240C.

EXAMPLE 3 A polyvinyl chloride pitch of softening point l50-l60 C. ismilled to l00 mesh and the resulting powder is extracted with 4 volumes(W/V) of a 10:1 (V/V) mixture of acetonebenzene at the freezing point ofthe solvent mixture. After stirring the mixture for one hour, the pitchis separated by decantation and the residue dried in vacuo. A secondsolvent mixture comprising pyridine-benzene, 20:1 (V/V) is added to thesolid pitch powder. The mixture is refluxed for 12 hours and thenfiltered. The filtrate is evaporated to dryness resulting i a spinnablepitch of softening point over 250 C.

EXAMPLE 4 A 52 APl light crude naphtha was subjected to catalytic Icracking at high pressure in the presence of steam to produce ethylene,other low boiling gases and a resinous residue having the followingproperties:

Softening point (Ring and Ball), C. 45

Specific gravity (at 15C.) 1.180 Conradson This residue has a darkbrown-black color and a glossy resinlike appearance. In an ASTM (13-20)distillation, 44 percent by weight of the material distilled. Ananalysis of the overhead showed it to be a highly aromatic materialcontaining substantial amounts of phenanthrene, anthracene, fluorene andvarious derivatives of these cyclic compounds.

A g. lot of this resin is dissolved in 4 liters of quinoline andfiltered through a pre-coat of 25 g. of activated carbon filter aid at100 C. in a steam jacketed fine porosity metal filter. The quinoline isremoved in vacuo. The resulting pitch is mixed with an equal volume ofbenzene and stirred in an indented flask at the reflux temperature ofbenzene for 4 hours. The pitch layer is separated by decantation of thebenzene layer. A vacuum is pulled on the flask for about 1 hour toremove the last traces of benzene and the pitch is ready for meltspinning.

EXAMPLE 5 is separated and conducted into a second catalytic crackingzone. The side stream of cycle oil therefrom is heated to a temperatureof 525 C. in a thermal cracking unit maintained at about 400 psi. Thevapors are stripped and recovered for gas and gasoline and the highboiling aromatic cut having the following characteristics is used asstarting material.

A.P.l. gravity 20 Distillation range 235 C. none 270 C. 16% 3 15 C. 34%355 C. 44% Residue 56% The above-defined starting material, 100 g. istriturated with 2.5 liters of a mixture of benzene-quinoline, 100:1(V/V), at about 5 C. for 20 minutes. The pitch is separated bydecantation of the benzene-quinoline solvent. The pitch is ground to l00 mesh and then added to another benzene-quinoline mixture, 2.5 litersof a 1:50 (V/V) solution at ambient room temperature. The solventeffects essentially complete solution. The solid particles are collectedtherefrom by adsorption on charcoal and centrifugation of the solids.

The solution is then evaporated to dryness to provide a spinnable pitch.

We claim:

1. A method for the preparation of a spinnable pitch which comprises a.grinding a pitch into small particles;

b. contacting the particles with an essentially aromatic or equivalentsolvent to dissolve a total of about to 30 percent therefrom;

c. separating the solvent and the insoluble particles;

(1. extracting the particles with a solubilizing solvent in sufficientquantity to dissolve at least 45 percent of the pitch based upon theoriginal quantity of starting pitch;

e. filtering the resulting mixture and f. evaporating the solvent fromthe resulting filtrate.

2. The process of claim 1 wherein the contacting step, b, is carried outat from about the freezing point of the solvent to about the softeningpoint of the pitch in contact with the solvent.

3. The process of claim 1 wherein the extracting step, d, is carried outat from about the freezing point of the solvent to about the refluxtemperature of the solvent.

4. A method for the preparation of a spinnable pitch which comprises a.extracting the pitch with a solubilizing solvent in sulfcient quantityto dissolve at least 45 percent of the pitch;

b. filtering the mixture;

c. evaporating the solvent from the resulting filtrate;

d. grinding the resulting pitch into small particles;

e. contacting the particles with an essentially aromatic or equivalentsolvent to remove a total of about 10 to 30 percent based upon theoriginal quantity of starting pitch therefrom;

f. separating the solvent and the particles.

5. The process of claim 4 wherein the contacting step is carried out atfrom about the freezing point of the solvent to about the softeningpoint of the pitch in contact with the solvent 6. The process of claim 4wherein the extracting step is carried out at from about the freezingpoint of the solvent to about the reflux temperature of the solvent.

' Patent No.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIGN 3,668,110 I DatedvJune 97 Frederick L. Shea et a1 'Inventor(s) It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

On the cover sheet insert [73] Assignee Greet Lakes Carbon Corporation,New York, N. Y.

signe and sealed this 12th day. of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. f ROBERT GO T'ISC HALK Attesting OfficerCommissioner of Patents USCOMM-DC GOING-P69 h u.s. GOVERNMENT PRINTINGOFFICE: 1959 o-3sa-3a4.

F ORM PO-105O (10-69)

2. The process of claim 1 wherein the contacting step, b, is carried outat from about the freezing point of the solvent to about the softeningpoint of the pitch in contact with the solvent.
 3. The process of claim1 wherein the extracting step, d, is carried out at from about thefreezing point of the solvent to about the reflux temperature of thesolvent.
 4. A method for the preparation of a spinnable pitch whichcomprises a. extracting the pitch with a solubilizing solvent insufficient quantity to dissolve at least 45 percent of the pitch; b.filtering the mixture; c. evaporating the solvent from the resultingfiltrate; d. grinding the resulting pitch into small particles; e.contacting the particles with an essentially aromatic or equivalentsolvent to remove a total of about 10 to 30 percent based upon theoriginal quantity of starting pitch therefrom; f. separating the solventand the particles.
 5. The process of claim 4 wherein the contacting stepis carried out at from about the freezing point of the solvent to aboutthe softening point of the pitch in contact with the solvent.
 6. Theprocess of claim 4 wherein the extracting step is carried out at fromabout the freezing point of the solvent to about the reflux temperatureof the solvent.